Vibratory mechanisms find wide use in construction and other applications. An example of such an application is a road compacting machine of the type having a cylindrical drum which rolls over freshly laid asphalt and which vibrates to compact the asphalt into a relatively hard surface suitable for vehicular traffic. An example of such a machine and a vibratory drum used therewith are disclosed in U.S. Pat. No. 4,577,995 (Sadahiro). And another example of a vibratory drum used for road compaction is disclosed in U.S. Pat. No. 4,586,847 (Stanton).
Road compaction represents but one way in which vibratory mechanisms are used. Such mechanisms also find utility in soil tillage. U.S. Pat. No. 3,627,056 (Rogers) discloses a multi-blade plow pulled by a farm tractor. The blades are vibrated by a rotating eccentric weight.
And as disclosed in U.S. Pat. No. 4,087,982 (Golobay), vibratory plows are used for underground placement (within a trench) of flexible cables, flexible pipelines and the like. Such placement is often referred to as "laying" a cable or pipeline.
Vibrating the plow blade results in a number of advantages including reduced disturbance of the earth, faster placement of the cable or pipeline and reduced drawbar pull, i.e., reduced force required to draw the blade through the earth. The benefits of reduced earth disturbance and faster installation are apparent. For a given plow blade, reduced drawbar pull can translate into reduced engine or vehicle size or, alternatively, into increased placement speed.
In many respects, the vibratory mechanism disclosed in the Golobay patent typifies the type of mechanism used with plows for underground placement. Such mechanism includes two eccentric weights, each affixed to a separate shaft. One of the weights is split into spaced-apart halves and the other weight passes between the halves as the weights rotate. Weight rotation is by direct motor drive to one of the shafts and by a belt, or other mechanized methods, to the second shaft; both shafts rotate in the same direction. But double-shaft-mounted weights which are gear-driven in opposite directions are also known.
While vibratory mechanisms of, for example, the type disclosed in the Golobay patent, have been generally satisfactory for the intended purposes, they are not without disadvantages. One disadvantage is that they are structurally large. This is so because the mechanism housing must be very sturdy to withstand the vibration and because the housing must be sufficiently large to accommodate two spaced shafts and their respective weights.
A related disadvantage is that they are heavy. And increased weight is often attended by increased manufacturing cost of the vibratory mechanism itself and by the need to "beef up" the supporting framework.
Yet another disadvantage relates to the way in which a vibratory cable-laying plow is sometimes used, namely, adjacent to building foundations or walls. A known type of mechanism (such as that disclosed in the Golobay patent) has a very significant lateral dimension, i.e., a dimension measured perpendicular to the plow direction of travel. This prevents the plow from being used as close to a building wall as it might otherwise be.
Still another disadvantage relates to productivity. For a given vehicle engine size, the energy available to do useful work, i.e., draw the plow through the earth, operate a cable reel or the like, diminishes as the size and weight of the vibratory mechanism and its supporting framework increase.
An improved vibratory apparatus which addresses disadvantages of earlier mechanisms would be an important technological advance.